I had a wonderful stay at Sue's place in Chateau In-Town. The unit features a kitchen with all the basics you need for cooking (including a toaster and rice cooker), a comfortable bed, and a window with a view of the Chao Phraya River. The unit was also sparkling clean when I arrived, which I really appreciated. The gym is on the same floor as the unit, which is also quite nice!
Although there are not many cafes or restaurants within close proximity, Double Slash coffee next door is excellent. 7-11 is nearby for all the basics, and there is often ample street food around. Rama 8 bridge is lovely to walk over in the early morning or evening. And it's a short cab ride from Chateau In-Town to Central Pinklao mall, which has everything you expect from a mall -- standard restaurants and shops, and Tops Grocery (good assortment of Western foods, for those who want them).
I stayed at Sue's place for several months while working nearby and was very satisfied. No complaints!